Perhaps the major function of neurons is the integrationof information impinging upon them from different sources. Since neuronal integraion is so important, one would expect to find a set of mechanisms during development that determines the number of different axons converging on each cell. In general, this number appears to be set postnatally in mammals by a competitive rearrangement of synaptic connections in which some initial innervation is lost (see Purves and Lichtman, 1980a). The goal of this proposal is to understand the factors that determine the number of axons that innervate individual neurons in mammalian autonomic ganglia. In particular, I want to explore the idea that competition between axon innervating the same cell is modulated be segregation on the postsynaptic surface of sets of terminals arising from each axon. The core of this idea is that confinement of innervation to a cell with few or no dendrites forces innervation from different axons of the sam class to copete; conversely, segregation of innervation to several different domains on a cell with dendrites reduces competition and allows multiple innervation to persist. The reason for carrying out these studies in autonomic ganglia is the relative simplicity of their organization. These aims will be pursued with electrophysiological, light, and electron microscopical methods in rabbit parasympathetic ganglia by 1) Intracellular marking of individual preganglionic axons; 2) Intracellular recording from and marking of individual ganglion cells with known numbers of inputs; 3) Double-labelling of pre- and postsynaptic elements; 4) In vivo recording of tonic and reflex synaptic activity in individual ganglion cells; and 5) Chronic alteratio of activity patterns of ganglion cells in early life. These approaches should provide a detailed picture of the way in which terminals from particular axons are distributed on individual postsynaptic neurons and how this distribution is affected by perturbations of neuronal activity. The significance of this work (and its long-term objective) lies in establishing the general rules that govern the formation and maintenance of synaptic connections in the mammalian nervous system.